X-ray tubes are known as an example of an X-ray radiation generator. To avoid voltage flashovers, it is necessary to insulate high voltage-conducting parts such as anodes from other parts in the vicinity by providing sufficient insulation.
For example, in order to increase insulation breakdown resistance, a housing of an X-ray tube may additionally have a sleeve built into it, which is composed of a dielectric material such as epoxy resin with quartz flour, ceramic, or PTFE, which essentially contains a bulb of the X-ray tube inserted therein and covers the X-ray tube radially relative to the housing. The additional dielectric material provides better electrical shielding or insulation of the anode of the tube from the surroundings. Alternatively, there are X-ray tubes in which the tubular housing of the tube is composed of a ceramic. The subassemblies for generating the X-ray radiation are contained in the housing. The anode of an X-ray tube heats up during operation; to avoid damage due to overheating, the heat is usually dissipated from the anode by means of a heat sink.
Heat sinks can be composed of a metal with high thermal conductivity such as aluminum or copper. In a heat sink composed of metal, in the part of the anode lying outside the housing of the X-ray tube, a minimum distance must be maintained between the heat sink and other components or housing parts connected to a reference potential (e.g. ground, GND, etc.) in order to prevent voltage flashovers. If the X-ray tube is to be operated with higher voltages, then this safety distance must be correspondingly increased. This can make it necessary to enlarge the outer housing of a system in which the X-ray tube is contained.
An insulation sleeve as mentioned above would impair the heat dissipation. Alternatively, it is possible to use a heat sink composed of a ceramic with good thermal conduction properties such as aluminum oxide or aluminum nitride. A heat sink composed of ceramic, however, is expensive to produce since special molds must be used. In addition, the metal of the anode—usually copper—has a higher thermal expansion coefficient than the externally mounted ceramic heat sink. This makes the heat transmission between the anode and the heat sink problematic: on the one hand, the heat sink should have the best possible heat conduction contact with the anode in order to achieve the highest possible heat transfer coefficient. On the other hand, the heat sink must be prevented from being damaged or even exploding due to the mechanical stress generated by the expansion of the anode when heated.
The design requirement “as compact as possible” is fundamental to many devices. The size of an X-ray radiation generator is limited at the lower end by the fact that certain components must be integrated into it and by the fact that the distances between the components that are contacted by a different electrical potential must be selected so that the breakdown resistance of the insulating mediums is not exceeded at any point.